"There are just more people riding and getting injured in that age group. It's definitely striking," says Dr. Benjamin Breyer, who led the study at the University of California, San Francisco.

Another study, published last month in the Morbidity and Mortality Weekly Report, found a similar trend with bicycle deaths: While the death rate among child cyclists has plummeted in the past four decades, the mortality rate among cyclists ages 35 to 54 has tripled.

Breyer isn't sure what's driving the surge in accidents among Generation Xers and baby boomers, but one reason could be what's known as the "Lance Armstrong effect."

"After Lance Armstrong had all of his success at the Tour de France, a lot more people were riding, and there were a lot more older riders that took up the bicycle for sport," he says.

The most recent National Household Travel Survey showed that the vast majority of the increase in bicycling between 1995 and 2009 came from Americans older than 25, with the biggest increases coming in the oldest groups. That has meant more men in their 50s and 60s on road bikes, riding at high speeds, Breyer says — a recipe for serious injuries.

"If you consider a 65-year-old who falls off their bike exactly the same way a 25-year-old does, the 65-year-old is going to sustain more injuries even if they're in great shape," he says.

But even that might not be enough, says Jason Vargo, who studies urban planning at the University of Wisconsin, Madison and led the recent study on bicycle deaths. He says society also needs to change the definition of what a road is to implicitly include bikers.

Some cities — like Madison, Wis., San Francisco and Portland, Ore. — are starting to do a better job at this.

But at the end of the day, reducing cycling accidents may boil down to something simpler: Making sure that bikers know the rules of the road — and that drivers know how to deal with bikers.

Copyright 2015 NPR. To see more, visit http://www.npr.org/.

Transcript

STEVE INSKEEP, HOST:

The other day, I was talking about riding a bicycle to work and somehow the conversation turned seamlessly from biking to disability insurance. More adults across this country are biking to work, which is good news for their hearts and their waistlines. But as NPR's Michaeleen Doucleff reports, it also means more visits to the ER.

MICHAELEEN DOUCLEFF, BYLINE: Today, Russell Lifson is one of a hundred or so bikers in San Francisco speeding down 17th Street on their way to work. But a few years ago, Lifson was literally on the pavement.

RUSSELL LIFSON: I was going through a stop sign by the Haight, and I did the full stop.

DOUCLEFF: And just then, a woman in a car pulled up to the stop sign next to him.

LIFSON: And then I looked at her, and she never really stopped. She pretended she was stopping.

DOUCLEFF: The woman went right through the intersection and - bam - T-boned Lifson, knocked him to the ground.

LIFSON: I'm fine, but she hit me pretty good, like, on the left side.

DOUCLEFF: Lifson's injuries were small enough that he didn't have to stay in the hospital and he was quickly back in the saddle. But Dr. Benjamin Breyer at the University of California, San Francisco, says many cyclists in the city aren't so lucky. Breyer is a urologist, and he often treats bike riders in the emergency room.

BENJAMIN BREYER: I see patients after they've had very significant traumas, so injuries to the genital, to the area where the bicycle seat rests - that area.

DOUCLEFF: Breyer kept seeing these injuries with cyclists, and he wondered if the problem went beyond San Francisco. So he analyzed data from about a hundred emergency rooms across the country. And right away, something jumped out at him - over the past 15 years, hospital emissions due to bike accidents had more than doubled. And the rise was the biggest in middle-aged bikers, those 45 and over.

BREYER: We saw very distinct patterns, that there are just more people riding and getting injured in that age group. It's definitely striking.

DOUCLEFF: Breyer and his colleagues report the findings this week in JAMA, the Journal of the American Medical Association. Another recent study found a similar trend with cycling deaths. They're on the rise with people aged 35 and over. Breyer thinks one reason for the surge in accidents is due to what's known as the Lance Armstrong effect.

BREYER: After Lance Armstrong had all of his success at the Tour de France, a lot more people were riding and there were a lot more older riders that took up the bicycle for sport.

DOUCLEFF: Which means more men in their 50s and 60s on road bikes riding at high speeds. And that, Breyer says, is a recipe for serious injuries.

BREYER: But I really do want to emphasize I think bicycle riding is fantastic. What a great way to get and then stay in shape. It's been shown to improve your overall well-being. It's been shown to reduce your overall mortality.

DOUCLEFF: But he says basic safety precautions are essential. Wear a helmet and reflective gear. Have lights for night riding. Drive defensively. And even then, it may not be enough.

JASON VARGO: It's not just the basics that will keep you safe.

DOUCLEFF: That's Jason Vargo. He studies urban planning at the University of Wisconsin, Madison. He says society needs to change the definition of what a road is.

VARGO: If you ask many people in this country of what a road is, they'll say it's a place where cars drive.

DOUCLEFF: But why shouldn't it be a place for cars and bikers to be? Vargo says some cities, like Madison, Portland, Ore., and here in San Francisco, are starting to do a better job at this.

VARGO: By slowing down speeds, adding protective places for cyclists, using different colored paint, more signs.

DOUCLEFF: And more education so drivers know how to deal with bikers and bikers know the rules of the road. Michaeleen Doucleff, NPR News. Transcript provided by NPR, Copyright NPR.